HYDROLOGIC RESPONSE OF A SUBURBAN WATERSHED TO CLIMATE MODELS

Abstract

Non-Point Source (NPS) pollution is an important issue in the Chesapeake Bay areas of the northeastern U.S. The TMDLs established by the Environmental Protection Agency requires a reduction in sediments, nitrogen and phosphorus by preset amounts, by 2025. One approach to meeting these requirements is to implement Best Management Practices (BMPs) for NPS pollution control. BMPs are most effective when implemented on areas named Critical Source Areas (CSAs) that contribute excessively to the pollutant load relative to their spatial extent. Studies have shown that climate change may have significant influence on the hydrology and water quality variables, and can therefore influence CSA identification in the future. In this study, six climate models were used for the evaluation of the hydrologic response of a suburban watershed in Maryland. The Soil and Water Assessment Tool (SWAT) was used for the model development, driven by the future climate from six models in four scenarios RCP2.6, RCP4.5, RCP6.0 and RCP8.5. Surface runoff, total suspended solids, total nitrogen and total phosphorus at the watershed outlet and on-land were assessed for two time horizons, mid-century and end-century. The simulations showed a significant increase of yields in all variables both in-stream and on-land among all models/scenarios/periods. CSAs identified using a relative threshold (eg. Top 20% of HRUs) did not vary markedly as climate was changed. However, CSAs identified using a fixed threshold increased substantially in area under future climate. Overall, results demonstrate the potential impacts of climate change on watershed hydrology across six models, and suggest that CSA identification based on relative threshold is most robust against future variability.